The manual includes the following:
To keep
the overview over the fraction of subtasks that are already completed, insert
either ‘[/]’ or ‘[%]’ anywhere in the headline. These cookies will
be updates each time the todo status of a child changes. For example:
* Organize Party [33%]This seems to mean that if I enter the following into an org file:
** TODO Call people [1/2]
*** TODO Peter
*** DONE Sarah
** TODO Buy food
** DONE Talk to neighbor